Democrat Walter F. Mondale carried the student vote yesterday in a mock presidential election conducted by District of Columbia and Prince George's County public schools.

Mondale's margin over President Reagan was almost 2 to 1 in the District, while in Prince George's he won 53.5 percent of the vote.

Although Mondale's margin of victory among District students was substantial, it was much smaller than the 10-to-1 edge in party registration that Democrats in the District hold over Republicans.

"The project has done what it's supposed to do," said Carolyn Preston, principal of the Bunker Hill Elementary School at 14th Street and Michigan Avenue NE, who coordinated the D.C. balloting. "We do not want the students to be swayed by their parents. We want them to think in terms of the year 2000 and make their own decisions."

According to Preston, Mondale received 19,199 votes citywide, compared to 10,599 for Reagan. In Prince George's, Mondale won by 7,653 to 6,297, with 341 votes cast for write-in candidates, according to James Kern, who served as coordinator there.

The mock electorate in the District included students from kindergarten through 12th grade. Preston said 92 of the city's 167 schools took part and more than a third of all D.C. students voted. The Prince George's vote was limited to students in grades seven through 12. Kern said 31 percent of the county's secondary schools participated.

Preston said Reagan carried the Northeast quadrant of the city by 6,891 to 3,713, but that Mondale swept everywhere else, winning by 2 1/2 to 1 in Southwest Washington and by about 5 to 1 in both Southeast and Northwest.